1. Field of the Invention
This invention relates to an optical type scanning microscope. This invention particularly relates to a scanning microscope, wherein a sample supporting member or an optical means for irradiating a light beam to a sample is supported on a tuning fork, and the tuning fork is caused to vibrate such that the sample may be scanned with the light beam. This invention also relates to a novel scanning mechanism.
2. Description of the Prior Art
Optical type scanning microscopes have heretofore been used. With the scanning microscope, a light beam is converged to a small light spot on a sample, and the sample is two-dimensionally scanned with the light spot. The light beam, which has passed through the sample during the scanning, the light beam, which has been reflected from the sample during the scanning, or the fluorescence, which is produced by the sample during the scanning, is detected by a photodetector. An enlarged image of the sample is thereby obtained. An example of the scanning microscope is disclosed in Japanese Unexamined Patent Publication No. 62(1987)-217218.
In the conventional optical type scanning microscopes, a mechanism which two-dimensionally deflects a light beam by a light deflector is primarily employed as the scanning mechanism.
However, the scanning mechanism described above has the drawback in that a light deflector, such as a galvanometer mirror or an acousto-optic light deflector (AOD), which is expensive must be used. Also, with the scanning mechanism described above, a light beam is deflected by a light deflector. As a result, the angle of incidence of the deflected light beam upon an objective lens of the light projecting optical means changes momentarily, and aberration is caused to occur. Therefore, the scanning mechanism described above also has the problem in that it is difficult for the objective lens to be designed such that aberration can be eliminated. Particularly, in cases where an AOD is utilized, astigmatism occurs in the light beam radiated out of the AOD. Therefore, in such cases, a special correction lens must be used, and the optical means cannot be kept simple.
In order to eliminate the aforesaid problems, a scanning mechanism has heretofore been proposed wherein a light beam is not deflected but a sample is scanned with the light spot of the light beam by two-dimensionally moving a sample supporting member. Also, in U.S. patent application Ser. No. 587,122, a novel mechanism has been proposed wherein a light projecting optical means and a light receiving optical means are supported on a single movable member, the movable member is moved while the a sample supporting member is kept stationary, and a light spot of a light beam is thereby caused to scan a sample.
In cases where the scanning with the light spot of a light beam is carried out by moving an optical means with respect to a sample supporting member, the optical means or the sample supporting member should be moved quickly such that the time required for an image of the sample to be formed may be kept short. For this purpose, by way of example, a piezo-electric device or an ultrasonic vibrator may be utilized as the drive source for moving the sample supporting member or the optical means.
However, in general, a device which can vibrate quickly has the drawback in that the amplitude of movement is small. A device which can vibrate with a large amplitude of movement has the drawback in that the speed of vibration cannot be kept high. If the amplitude of movement is small, the width, over which the light spot of the light beam scans a sample, must be set to a small value, and therefore a microscope image of a large area of the sample cannot be obtained.
In cases where a microscope image of a large area of a sample cannot be obtained, considerable time and labor are required to find the part of the image, which it is necessary to reproduce ultimately as a visible image, i.e. to find the field of view. In order for a microscope image of a large area of the sample to be reproduced, a plurality of images of a small areas of the sample may be combined and a composite image may thereby be reproduced. However, in such cases, a long time is required to carry out the combining process, and therefore the time required for a microscope image to be reproduced cannot be kept short. Also, in such cases, if the positions of the plurality of the images to be combined are adjusted accurately, the problem will occur in that joints between the images thus combined appear in the composite image.
In cases where the magnification, with which a microscope image is formed, is to be changed in the aforesaid optical type scanning microscopes, an objective lens has heretofore been exchanged as in ordinary nonscanning types of microscopes. Alternatively, a zoom lens incorporated in the microscopes has heretofore been operated as in ordinary non-scanning types of microscopes. However, with these techniques, considerable time and labor are required to carry out such operations, and the operating efficiency of the scanning microscopes cannot be kept high.
When a sample supporting member or an optical means is moved by a piezo-electric device, an ultrasonic vibrator, or the like, the magnification, with which a microscope image is formed, can be altered by changing the amplitude of movement. However, as described above, with such a device, it is difficult for the amplitude of movement to be kept large. When the amplitude of movement is small, the scale of reduction or enlargement of the image cannot be kept large.
Also, in the course of periodically sampling the output of a photodetector in accordance with a sampling clock signal (i.e. a pixel clock signal), the magnification, with which a microscope image is formed, can be altered by changing the frequency of the sampling clock signal.
However, in such cases, particularly when a piezo-electric device is employed, a hysteresis occurs with the drive voltage vs. displacement characteristics, and the hysteresis curve varies markedly in accordance with the amplitude, temperature, or the like. In order to cope with the variation in the hysteresis curve, the drive voltage waveform for the piezo-electric device and the timing, with which a sampling clock signal is generated, must be changed in accordance with the amplitude, temperature, or the like. Therefore, the scanning microscope cannot be kept simple in configuration, and the cost thereof cannot be kept low.